Computed tomography (CT) is a medical imaging method in which an X-ray apparatus scans an object of interest, for example a patient, and takes a series of X-ray images. From the series of X-ray images, a three-dimensional image of the inside of the object may be generated with the aid of digital geometry processing methods. As a rule, the series of pictures is taken during the movement of an X-ray imaging device about an axis of rotation. The volume data encoding the three-dimensional image of the object of interest may further be manipulated, for example it may be processed to be displayed as slices of the object of interest on a display device. Generally, various structures inside the object of interest may be visualized based on the ability of the structures to block an X-ray beam from the X-ray imaging device.
CT is a very useful tool in supporting the diagnosis of cancer. In particular, for the diagnosis of a hepatocellular carcinoma (HCC) in a first phase of the procedure a contrast agent may be injected into the liver of a patient and after a waiting period the liver is scanned for the first time. In a second phase of the procedure, again a contrast agent is injected into the liver and after a second waiting period that is longer than the waiting period before the first scan, the liver is scanned a second time. By comparing the two scans, a physician may be supported in the diagnosis of a hepatocellular carcinoma. In the scan of the first phase both a HCC and pseudo lesions (like arterioportal shunts) are visualized due to the contrast agent. In the scan of the second phase, a HCC generally shows ring-like enhancements, which is not expected for pseudo lesions, allowing to distinguish HCC a from other structures and lesions of the liver. The ring-like structure shows up in the images, since HCC is a type of tumour that comprises small vessels surrounding the tumour which are filled by the contrast agent dispersing inside the liver after a certain time corresponding to the second waiting period after the second contrast agent injection.
The time period after which the contrast agent reaches the small vessels may be short. Therefore, a conventional computer tomography apparatus may not be able to execute two scans of the patient while the contrast agent is dispersing inside the liver up to the small vessels. This is the reason why, conventionally, the contrast agent is injected two times during the diagnosis.
However, injecting two times a contrast agent may be a great stress for the patient. Further, the whole procedure may become very time-consuming.